Gain adjust circuits are often employed at the input of various communication systems for adjusting the amplitude of an input signal. In most voice processors, a voice operated gain adjust circuit (VOGAD) is usually found in the analog audio input section of the system. The VOGAD monitors the amplitude of voice signals in the input signal and multiplies the input signal by a gain factor such that the voice signals are at a desired amplitude level for further processing in the voice processor.
Voice processor systems often employ a hand set with a push-to-talk control button. In this type of system, conventional VOGADs provide adequate performance by keying their operation to the signal from the push-to-talk control button. Usually, the VOGAD is enabled when the button is depressed. However, in many commercial environments of voice processors, push-to-talk type control is not used. In commercial environments, such as in a telephone system interface or in computer room applications, a high level of background noise may be present.
Background noise and changing input levels have been found to interfere with the operation of most known conventional VOGADs. In such noisy environments, conventional VOGADs often overamplify or underamplify the input signal to the voice processor so that the voice signal is not at a desired amplitude.
Thus, a need has arisen for a new VOGAD capable of performing properly in a noisy environment in which an input signal includes background noise as well as the desired signal. In particular, a need is felt for a VOGAD that distinguishes between voice signals and background noise and that is capable of amplifying the input signal to the voice processor in response to the amplitude of the voice signals alone.